I have the same problem. My printer based on EPSON R1800. I think I have to buy a new printhead in order to be able to print white ink again
It was totally my fault. I'd been doing nozzle check and seen that the white ink pattern was good so I didn't keep printing white ink at least one t-shirt a day. Finally, suddenly, one day it just clogged and too late to fix it.
Anyways, Good luck with your printer!
